Arrangement for damping vibrations in the bearings of rotatable shafts

ABSTRACT

Cryogenic helium expansion turbine shaft and bearing lubricated by injecting gas under pressure, wherein the bearing comprises recesses regularly spaced around the periphery of the bearing, the recesses being provided with tubes which connect them with the other recesses through an annular groove formed in the bearing.

United States Patent [72] Invented Pierre Giro! [50] Field of Search...".1 "308/9, 122, Paris, France r v 120 [2 l] Appl. No. 810,475 [22] FiledMar. 26, 1969 6] References C|ted [45] Patented Aug. 31, 1971 UNITEDSTATES PATENTS 1 As s L'Air Liquids Anonyme p 2,449,297 9/1948 Hoffer308/122 lEtude g i a p des Procedes 2,459,825 1/1949 Martellotti 308/122[32] Priority e Primary Exariziner-Frederick L; Matteson I l 33] Fral'meAssistant ExaminerFrank Susko l 31 1 148044 Attorney-Young & ThompsonABSTRACT: Cryogenic-helium expansion turbine shaft and [54) IN bearinglubricated by injecting gas under pressure, wherein 7 Ch 5D in thebearing comprises recesses regularly spaced around the raw 2 peripheryof the bearing, the recesses being provided with [52] US. Cl 308/122tubes which connect them with the other recesses through an [51] Int. ClF 16c 1/24 annular groove formed in the bearing. 1

445., 53 r c 6 B PATENTED mm I97! 3502' 557 SHEET 2 0F 2 P/bans) min.

Avnswrae Paw/e5 'neor ARRANGEMENT FOR DAMPING VIBRATIONS IN THE BEARINGSF ROTATABLE SHAFIS This invention relates to an arrangement for dampingvibrations in the bearing of rotatable shafts. More particularly, theinvention is concerned with an arrangement for damping vibrations, oroscillations, in a hearing which is lubricated by injecting gas underpressure into a space formed between the shaft and the hearing frominjection ducts arranged in the bearing or the shaft and wherein thebearing or the shaft has recesses disposed opposite said space, thenumber of which is a multiple of, is equal to or is a submultiple of thenumber of injection ducts, the angular offsetting of the recessesbetween themselves and relatively to the injection ducts being constant.

Such bearings are used to support rotatables shafts of machines, moreparticularly for shafts which are required to rotate at high speeds ofup to several hundred thousand revolutions per minute, for example smallgas expansion turbine for machines for the production of cold at lowtemperature and more particularly for the liquefaction of hydrogen orhelium. Bearings of this type are generally referred to as hydrostaticgas bearings. These gas bearings enable there to be obtained rotationalspeeds very much higher than those obtained with normal bearings, butthey exhibit, at a certain fairly high rotational speed, vibrationswhich may be amplified and cause them to seize. This kind of vibrationis generally referred to as half-speed whirl."

It has already been proposed to clamp these vibrations, or oscillations,by providing each of the conduits for supplying gas towards theinjection recesses with a constriction and a chamber connected inseries, or to arrange in the bearing both injection ducts and chambersfor discharging gas towards the ambient atmosphere, followed byconstrictions, or other devices for 90 phase displacement between thegas delivery and the pressure in the injection ducts opposite therotating shaft, so as to produce a pressure maximum in a gasintroduction duct at the instant when the shaft is in its centralposition and is displaced towards the said duct. Such devices, however,result in considerable gas consumption rates and are relativelycomplicated.

It is an object of the invention to obviate the aforesaid disadvantagesand to permit effective damping of the oscillations of a shaftrelatively to its bearing and, consequently, to achieve relatively highrotational speeds with a low gas consumption.

Thus, in accordance with the invention there is provided and arrangementfor damping vibrations in the bearing of a shaft adapted to rotaterelative to the bearing, wherein the bearing is lubricated by injectinggas under pressure into a space formed between the shaft and thebearing, from gas injection ducts arranged in the bearing or the shaft,wherein the bearing or the shaft comprises recesses opposite said space,the number of which is a multiple of, is equal to or is submultiple ofthe number of injection ducts, and wherein angular offsetting of therecesses relatively to one another and relatively to the injection ductsis constant, characterized in that at least two of the recesses, whichhave a constant angular spacing from one another, are connected to oneanother by at least one conduit which does not form part of the pressuregas dis tribution network and is different from the bearing clearance,said conduit being of small diameter over at least a part of its length.

Advantageously, the invention also comprises the following featurestaken separately or in any'combination thereof:

a. the recesses are arranged in the bearing which is fixed, and theconduit of small diameter which connects some of these recesses isconstituted, inside the bearing, by radial tubes and a circular grooveformed in the body of the bearing and concentric therewith;

b. the number of recesses connected together is at least three;

c. n groups of recesses exist which are connected respectively to oneanother by n conduits, and these groups are angularly offset relativelyto oneanother by an angle equal to the fraction lb: of the angle formedbetween the center and the radial axes of two successive recesses of thesame group;

d. at least a proportion of the injection ducts debouch into recesseswhich are regularly distributed over the periphery of the bearing or ofthe shaft;

e. at least a proportion of the recesses,which are uniformly distributedover the periphery of the bearing or of the shaft, are not connected toany injection duct;

f. the recesses are arranged on the rotatable shaft adjacent thebearing, and the conduit of small diameter which connects some of theserecesses is constituted by radial tubes formed in the body of the shaft.

For a better understanding of the invention, and to show how the samemay be carried into effect, reference will now be made, by way ofexample, to the accompanying drawings, in which:

FIG. 1 is a sectional view of a simplified stabilization arrangementalong a vertical diameter of the bearing and illustrating the principleon which the invention based, the section being taken through a planeperpendicular to the axis of the shaft;

FIG. 2 is a sectional view, similar to that of FIG. 1, of one embodimentof a stabilization arrangement in accordance with the invention;

FIG. 3 is a sectional view, similar to that of FIG. 1, of a secondembodiment of a stabilization arrangement in accordance with theinvention applied to a cryogenic helium expansion turbine;

FIG. 4 shows the stabilization arrangement of FIG. 3 viewed as a sectiontaken through a diameter plane, this plane being assumed for simplicityto contain both axes of two apertures for introduction of gas underpressure and two apertures for balancing which are connected to aconduit joining a group of recesses; and

FIG. 5 is a diagram showing the variation in the critical speed ofrotation (above which nondamped vibrations appear) of the shaft of thedevice shown in FIGS. 3 and 4 as a function of the relative pressure ofthe injected helium and, by way of comparison, the variation of thissame critical speed of rotation in the case of a similar shaft whosebearings are not provided with the stabilization arrangements of theinvention.

Referring first to FIG. 1, there is shown a stabilization arrangement inwhich a shaft 1 is arranged within a bearing 20 so as to leave aclearance 3 in which gas circulates. The gas is injected, by way ofducts (not shown), into recesses 4A and 4B and penetrates into theclearance between the shaft and the bearing as indicated by the arrowsf. The recesses 4A,4B are connected by tubes 5A and 58 to a balancingconduit 6. the diameters of the tubes and conduit being exaggerated forthe sake of clarity.

If it is assumed that at a given instant ina vibration, the shaft 1 isdirected towards the recess 4A, as indicated by the vertical arrow onthe shaft 1, it will be understood that the gas which is compressed inthe recess 4A escapes through the tube 5A into the conduit 6, while thereduced pressure which occurs in the chamber 48 causes the entry intothe said chamber by way of the tube 53 of a portion of the gas containedin the conduit'6.

Naturally, a device of this kind provides stabilization only along thediameter which passes through recesses 4A and 4B, and cannot be usedsimply in this form. It is necessary to add a similar arrangement forstabilization along a diameter perpendicular to the diameter whichpasses through recess 4A and 48. Alternatively, there can be constructedan arrangement in which at least three recesses are spaced uniformlyaround the periphery of the bearing.

FIG. 2 shows stabilization arrangement having three recesses spacedatintervals around the periphery of the bearing, thereby effectingsatisfactory stabilization of the shaft 1. More particularly, itcomprises the recesses 4A, 4B and 4C,

which are provided with tubes 5A, 5B and 5C, each of which connects itsassociated recess with an annular groove 6 formed in the bearing. Theintroduction of a gas under pressure into the recesses 4A, 4B and 4C iseffected by way of ducts, not shown in the illustration, which arearranged, for example, above or below the plane of FIG. 2.

Turning now to FIG. 3, there is shown a stabilization arrangement havingsix balancing recesses spaced at 60 intervals around the periphery ofthe bearing for the stabilization of a shaft of a small cryogenic heliumturbine. The clearance between the shaft and the bearings has beenexaggerated for greater clarity. The recesses 4A, 4B, 4C, 4D, 4E and 4Fare provided with ducts 7A to 7F, only a part of the ducts being shown,for the injection of helium under pressure. As shown in FIG. 4, which isthe same device in diametral section, each gas injection duct, forexample duct 7A, comprises a plurality of successive bores the diameterof which increases towards the exterior. The injection ducts areconnected to supply conduits, for example duct 7A is connected toconduit 9A. Six other ducts, 8A to SF, are arranged in the bearingbetween the ducts connected to the recesses 4A to 4F, and spaced at 60intervals, with an angular offsetting of 30.

In one specific embodiment of the type shown in FIGS. 3 and 4 the shafi1 had a diameter of 14 mm. and a length of 8.4 mm. engaging the bearing,the recesses 4A to 4F had, for example, a depth of 0.02 mm. and a widthof 5 mm. and they each subtended an angle of 25 at the center of theshaft. The helium injection ducts had a diameter of 0.30 mm. in thevicinity of the surface of the bearing. The tubes 5A to SF had adiameter of 0.25 mm. in the vicinity of the corresponding recess, thenincreasing to 0.30 mm. They were connected to annular grooves 6A and 68formed in the bearing (the diameters of the circles described by thegrooves 6A and 6B formed in the bearing (the diameters of the circlesdescribed by the grooves 6A and 6B are shown as being different in FIG.3 to enable them to be distinguished from one another, but they are iiireality of equal diameter). These grooves have for example rectangularcross section of 0.5 X0.5 mm. with a circle diameter of 39 mm.

FIG. 5 shows the variation of the critical stable speed (in revolutionsper minute) as a function of the effective pressure (in bars) at whichthe helium is injected for, on the one hand, a system having 12injection apertures but without the stabilization arrangement accordingto the invention (brokenline curve) and, on the other hand, for a systemhaving the stabilization arrangement according to the invention which isillustrated in FIGS. 3 and 4 (full-line curve). It will be observed thatthe stabilization arrangement according to the invention makes itpossible to achieve a notably higher rotational speed for a givenpressure of injected helium (the critical speed being more than doubled)or the same critical stable speed for a notably lower helium injectionpressure (for example a speed of approximately 1 10,000 revolutions perminute with an injection pressure 3 bars effective instead of 6.5 bars).The consumption of helium for the same critical stable speed istherefore considerably reduced.

It will be understood that various-modifications may be made to thestabilization arrangements which have just been described within thescope of the present invention. More particularly, although a moredifficult constructions, it is possible to arrange the gas injectionducts and balancing conduits in the rotation shaft itself and not in thefixed bearing.

The invention can also be applied to machines having shafts rotating ata high speed, for example rotary compressors, gyroscopes andcentrifuges. It can also be applied to conical or spherical hearings orthrust bearings.

Having described my invention I claim:

1. In a bearing assembly comprising a bearing and a shaft rotatablerelative to the bearing, the shaft and bearing having a spacetherebetween for lubrication by gas under pressure, recesses in one ofsaid bearing and shaft opening into said space, said recesses beingdisposed symmetrically about the axis of the shaft and being spacedequal angular distances about the axis of the shaft, one of said bearingand shaft having supply ducts therein for supplying gas under pressureto said space; the improvement comprising at least one duct in one ofsaid bearing and shaft interconnecting at least two of said recesses,said-duct being entirely spaced from said 2 ducts and entirely spacedfrom said space and having a least width substantially less than thewidth of the recesses.

2. An assembly as claimed in claim 1, said recesses and ducts beingdisposed in said bearing.

3. An assembly as claimed in claim 2, said interconnecting ductcomprising radially disposed portions that communicate with saidrecesses and a circular groove in the bearing that interconnects saidradially extending portions.

4. An assembly as claimed in claim 1, the recesses interconnected bysaid interconnecting duct being at least three in number.

5. An assembly as claimed in claim 1, said supply ducts emptying intosaid recesses.

6. In a bearing assembly comprising a bearing and a shaft rotatablerelative to the bearing, the shaft and bearing having a spacetherebetween for lubrication by gas under pressure, recesses in one ofsaid bearing and shaft opening into said space, said recesses beingdisposed symmetrically about the axis of the shaft equal angulardistances about the axis of the shaft, one of said bearing and shafthaving supply ducts therein for supplying gas under pressure to saidspace; the improvement comprising at least one duct in one of saidbearing and shaft interconnecting at least two of said recesses, saidduct being entirely spaced from said gas-supply ducts and entirelyspaced from said space and having a least width substantially less thanthe width of the recesses, said recesses being arranged in at least twogroups with the recesses of each group interconnected by a saidinterconnecting duct, adjacent groups being offset from each other byequal angles.

7. An assembly as claimed in claim 1, the areas of said recesses thatopen into said space being substantially equal to each other.

1. In a bearing assembly comprising a bearing and a shaft rotatablerelative to the bearing, the shaft and bearing having a spacetherebetween for lubrication by gas under pressure, recesses in one ofsaid bearing and shaft opening into said space, said recesses beingdisposed symmetrically about the axis of the shaft and being spacedequal angular distances about the axis of the shaft, one of said bearingand shaft having supply ducts therein for supplying gas under pressureto said space; the improvement comprising at least one duct in one ofsaid bearing and shaft interconnecting at least two of said recesses,said duct being entirely spaced from said 2 ducts and entirely spacedfrom said space and having a least width substantially less than thewidth of the recesses.
 2. An assembly as claimed in claim 1, saidrecesses and ducts being disposed in said bearing.
 3. An assembly asclaimed in claim 2, said interconnecting duct comprising radiallydisposed portions that communicate with said recesses and a circulargroove in the bearing that interconnects said radially extendingportions.
 4. An assembly as claimed in claim 1, the recessesinterconnected by said interconnecting duct being at least three innumber.
 5. An assembly as claimed in claim 1, said supply ducts emptyinginto said recesses.
 6. In a bearing assembly comprising a bearing and ashaft rotatable relative to the bearing, the shaft and bearing having aspace therebetween for lubrication by gas under pressure, recesses inone of said bearing and shaft opening into said space, said recessesbeing disposed symmetrically about the axis of the shaft equal angulardistances about the axis of the shaft, one of said bearing and shafthaving supply ducts therein for supplying gas under pressure to saidspace; the improvement comprising at least one duct in one of saidbearing and shaft interconnecting at least two of said recesses, saidduct being entirely spaced from said gas-supply ducts and entirelyspaced from said space and having a least width substantially less thanthe width of the recesses, said recesses being arranged in at least twogroups with the recesses of each group interconnected by a saidinterconnecting duct, adjacent groups being offset from each other byequal angles.
 7. An assembly as claimed in claim 1, the areas of saidrecesses that open into said space being substantially equal to eachother.